1. Field of the Invention
This invention relates to an engine control apparatus for controlling a condition of an internal combustion engine and particularly to an engine control apparatus for controlling an engine speed of an internal combustion engine at idling operation and an engine control apparatus for controlling an air fuel ratio of an internal combustion engine.
2. Description of the Prior Art
As one of engine control apparatus, an idling engine speed control apparatus is known which uses the so-called modern controlling technique where a control amount of an auxiliary air control valve or the like is operated in accordance with an optimal feedback gain predetermined by a simulation with an estimation function or the like and with a state variable amount representing an internal condition of an engine. It controls the engine speed of an internal combustion engine to a target speed by determining an air flow rate of the idling operation from a detected engine speed through a dynamic model of the engine such technique is disclosed in, for example, Japanese patent application provisional publication No. 64-8336 whose corresponding application is U.S. Pat. No. 4,785,780.
However, in the apparatus mentioned above, there is a problem that hunting occurs as shown in FIGS. 11A, 11B, and 11C showing controlled conditions according to the prior art engine control apparatus because the engine speed is not properly controlled if the control mentioned above is carried out in the condition that an air fuel ratio deviates from an theoretical air fuel ratio (for example, in the over-rich or over-lean conditions), that is, in the condition that an model error will occur because the dynamic model mentioned above is determined on the assumption that the air fuel ratio is within a theoretical air fuel ratio range.
It is necessary to determine a dynamic model including the air fuel ratio factor in order to prevent this hunting. However, there is a problem that much manpower is required for determining the feedback constants if the model is determined with the air fuel factor included in the dynamic model, that is, the model is determined with an addition of an input. Moreover, there is a problem that a load to an electric control portion will increase because much storing capacity is necessary to store feedback gains in accordance with respective engine conditions.